1. Field of the Invention
The present invention relates to a hinge for foldable ladders having an improved locking device with a rectangular locking block and a press locking control device with a pressing member. More particularly, the pressing member elastically contacts the rectangular locking block for controlling the operation of ladders. The hinge mechanism innovates by replacing the parts that may cause a malfunction and provides a secondary safety device for the secured operations.
2. Description of the Prior Art
Referring to FIG. 1 and FIG. 2 of the U.S. Pat. No. 4,770,559 (Issue Date: Sep. 13, 1998, Title: Positioning joint for folding ladders), it discloses a conventional hinge comprising a first joint member (10), second joint member (20) being installed inside of disc (23) of the first joint member (10), locking device (30), and guide disc (40). The first joint member (10) comprises two main discs (13, 14) formed with axial hole (12) at a center. The second joint member (20) having a sub-disc member (23) will be inserted between the two main discs (13, 14). The sub disc member (23) forms a rectangular slot (25), coil retaining hole (26), protrusion (27) and a plurality of detents (28) being formed around the periphery. A guide disc (40) is provided with a coil spring (29), retaining hole (46), a plurality of detents (48) formed around the periphery, a rectangular slot (45) and an arcuate slot opening (47). An end of the coil spring (29) is hooked at the coil retaining hole (26) of the sub disc member (23) and the other end is hooked at the coil retaining hole (46) of the guide disc (40).
A locking device (30) comprises a button (32), rectangular locking block (33), and connecting pin (31). The locking device (30) is elastically moved up by the coil spring (29) through the slot openings (35, 36) being formed at the main disc (13, 14) of the first joint member (10).
The first and second joint members (10, 20) are combined by a common axis of a center shaft (50) enabling relative rotation. The coil spring (29) being linked to the second joint member (20) and the guide disc (40) is installed inside of the first joint member (10). According to the interactions between the protrusion (27) and the arcuate slot opening (47), a locking device (30) of the first joint member (10) is selectively latched to the detent (28) located at the periphery of the sub disc (23) of the second joint member (20) under a controlling of the guide disc (40). The locking and unlocking position of the locking device (30) is determined and maintained at preset angular positions by the guide disc (40).
In order to adjust the angular positions of the joint members (10, 20), i.e., for folding or unfolding the ladders, the rectangular locking block (33) must be pulled out from the main disc (14) for disengaging the detent (28) of the second joint member (20) by pushing the button (32) of the locking device (30). Then, the ladder enables to adjust the angular position of the joint members (10, 20) to fold or unfold.
Due to the repeated interactions of the first and second joint members (10, 20), the coil spring (29) being installed between the first and second joint members (10, 20) will contact the inner surface of the main disc (14) accompanied by friction. Thereby, the coil spring will be deformed or broken due to the consistent friction with the interior surface of the main disc (14). If the coil spring (29) is contaminated by a foreign object such as dust, the first and second joint members will not properly operate or get damages. If the ladder is consistently operated with the default, the guide disc (40) will continuously become deformed or twisted by the torsion stress. As a result, the first and second joint members will become completely damaged and will not work.
Also, when the ladder receives an external impact or load, the force will transmit to the hinge parts. The sudden impact or load will damage or deform the hinge of ladders. The conventional ladders having a large clearance have a disadvantage of unstableness and do not properly support the sudden load.
Such a problems as mentioned above could be a potential danger. If an accident occurred due to a malfunction of the hinge, a user would get an injury. Thus, those problems must be solved for improving secured operations of ladders.
A hinge for foldable ladders of the present invention comprises a first joint member (10) integrally formed with the main discs (13, 14), a second joint member (20) integrally formed with a sub disc (23), a locking device (30) having a button (32), a connecting pin (31), a coil spring (34), and a rectangular locking block (33) and a press locking control device (60) for controlling the latching or unlatching of the locking device (30). The first and second joint members (10, 20) are combined together through a common axis of a center shaft (50) enabling rotation. The sub disc (23) of the second joint member (20) is inserted between a pair of parallel spaced main discs (13, 14) of the first joint member (10). The main discs (13, 14) of the first joint member (10) have slot openings (13a, 13c) for inserting the locking device (30). The first protruded arcuate stopper (15) is disposed at the inner surface of the main disc (14). The second protruded arcuate stopper (25) is formed at the rear surface of the sub disc (23) of the second joint member (20) for matching with the first protruded arcuate stopper (15) of the main disc (14). A plurality of detents (28) is formed around periphery of the sub disc (23). At one side of the slot opening (13c) of the main disc (14), a press locking control device (63) is installed for elastically actuating the device.
As an alternative embodiment of the present invention, a hinge for foldable ladders comprises the first joint member (210) having a couple of common holes (224, 234) at the main discs (213, 214), the second joint member (240) with six piercing holes (244) at the sub disc (223), a center shaft (50) for mounting the first and second joint members, a locking device (260) having a protruding pin (262) integrally formed with the center shaft (50) and installed through the main and sub discs (213, 214, 223), and a pressing member (63) installed lateral of the hole (234) at the main disc (214) of the first joint member (210) for elastically actuating and controlling the back and forth movement of the protruding pin (262) of the locking device (260).